Buy it and put a big-bore Blaster engine in there!!
If you decide to get it, like others have said, you are taking your chances. Part of the worry is that when a 4 stroke engine blows a top end, it usually goes boom. Things often get ugly in there when you tear it down for inspection, unlike on a Blaster when the worst damage is often limited to the piston/rings and cylinder.
The 4 stroke engines in these Suzuki's use shim-and-bucket valve adjusters, if Im not mistaken. In other words, the valves tighten up over time due to seat wear, and if they don't get adjusted often enough, the valve will extend too far into the cylinder, only to be hit in the head by the piston. And then you've got an engine with the dreaded ($$$ to fix) "dropped valve". Im not a 4-stroke guy, but it seems Suzuki engines like to drop more valves than other brands.
My neighbor across the street had a big-bore Suzuki dirtbike, and I used to listen to him ride. I could tell that the engine was running poorly. I warned him to get his valves adjusted. He ignored my advice, dropped a valve a month later, and sold the bike.
Moral: Buyer beware. A cracked head and/or broken valves get expensive to fix real quick. And that doesnt include necessary parts such as the cam chain, piston, gasket set, etc. You never know what you are buying until you tear it down for inspection. The best "blown" 4 stroke to buy is one that still runs, but smokes badly. Much of the time, smoking can be cured without touching the head.